The desktop and laptop world is dominated by x86, the mobile/embedded world by ARM. Conventional wisdom, right? Not really. There's also MIPS - hundreds of millions of embedded devices run on MIPS, and for years now, the architecture has been trying to break into the mobile world dominated so much by ARM. They just a got a boost: MIPS has been acquired by Imagination Tech, most known for its PowerVR graphics chips used in a lot of smartphones and tablets.

I am the author of the open source PlayStation development kit, the PSXSDK. No support for 3D operations and broken memory card support right now, but otherwise functional.
Check it out: http://code.google.com/p/psxsdk
You can run it on any estabilished operating system because it is based on off the shelf gcc/binutils.